Vapor stripping method

Abstract

Coatings, such as paint or oil, are stripped from the surface of a coated object by circulating a stream of a stripping composition in a gaseous state at ambient temperature and pressure into contact with the surface. The stripping composition is normally a liquid at ambient temperature and pressure and has a partial pressure of at least 5 mm of Hg. at ambient conditions. The contacting procedure is conducted substantially in the absence on the surface of liquid condensate of the stripping composition.

What we claim as new and desire to be secured by Letters Patent is: 
     
       1. A method for stripping a protective coating from the surface of a coated object, comprising circulating a stream of a stripping composition in a gaseous state at about ambient temperature and pressure into contact with said surface for a time sufficient to destroy the adhesion between said protective coating and said surface and substantially in the absence on said surface of liquid condensate of said stripping composition, said stripping composition normally being a liquid and having a partial pressure of at least about 5 mm. of Hg. at ambient temperature and pressure. 
     
     
       2. A method according to claim 1 in which said stripping composition comprises a lower chloroalkane and the method is carried out without heating said stripping composition to reflux temperature. 
     
     
       3. A method for stripping a protective coating according to claim 1 and the further step comprising: sealing said surface from the atmosphere in a stripping zone.   
     
     
       4. A method for stripping a protective coating according to claim 3 and the further steps comprising: withdrawing at least a portion of said air in said stripping zone so that the gas phase in said stripping zone is enriched with said stripping fluid and   circulating said gaseous state stripping composition within said stripping zone.   
     
     
       5. A method for stripping a protective coating according to claim 4 wherein from a major portion to substantially all of said air is withdrawn from said stripping zone so that the atmosphere in the stripping zone is mainly stripping gas, the pressure of which is such that substantially no liquid condensate forms on the surface being stripped. 
     
     
       6. A method for stripping a protective coating, according to claim 3 and the further steps of: passing a stream of air over said paint stripping composition in an evaporation zone to produce a stream of said paint stripping composition in the gaseous phase,   introducing the thus formed stream of said stripping composition in the gaseous phase into said paint stripping zone and withdrawing at least a portion of the air from said paint stripping zone, whereby the gas phase in said gas stripping zone is enriched with said stripping composition.   
     
     
       7. A method for stripping a protective coating according to claim 6 wherein from a major portion to substantially all of said air is withdrawn from said stripping zone so that the atmosphere in the stripping zone is mainly stripping gas, the pressure of which is such that substantially no liquid condensate forms on the surface being stripped. 
     
     
       8. A method for stripping a protective coating according to claim 6 and the further steps comprising: continuously withdrawing said stripping composition in the gaseous state from said stripping zone,   continuously recycling said stripping composition in the gas phase which has been withdrawn from said stripping zone back to said stripping zone until the adhesion between said protective coating and said surface has been substantially destroyed and then,   withdrawing substantially all of said stripping composition in the gaseous state from said stripping zone.   
     
     
       9. A method according to claim 1 in which said stripping composition is comprised of about 25 to 100% by volume of methylene chloride. 
     
     
       10. A method according to claim 1 in which said paint stripping composition consists essentially of a mixture of methylene chloride as the principal ingredient and at least one additional component selected from the group consisting of water, ammonia, lower alkylamine, lower carboxylic acid, lower alkanol, lower alkyl ether, lower alkyl ester, lower alkyl nitrile, lower carboxylic acid amide and lower alkyl amide, lower alkane, lower alkyl ketone and benzene and lower-alkyl and halogen substituted benzene, heteroaromatic compounds containing up to 8 carbon atoms and volatile inorganic acids, wherein said component has a vapor pressure of at least about 5 mm. of Hg at ambient temperature. 
     
     
       11. A method according to claim 10 in which said stripping composition contains by volume about 70 to 95% of methylene chloride and 5 to 30% of said additional component and wherein said additional component includes at least about 1% of water. 
     
     
       12. A method according to claim 10 in which said stripping composition contains by volume about 70 to 90% of methylene chloride and 10 to 30% of 33 to 75% aqueous ethylamine. 
     
     
       13. A method according to claim 10 in which said stripping composition contains by volume about 70 to 95% of methylene chloride about 1% of water and an additional component selected from methyl alcohol and methyl ethyl ketone. 
     
     
       14. In a method of stripping a protective coating from interior coated surfaces of large constructions, including in particular the interiors of storage tanks on land and holds and ballast tanks of ships, the steps comprising: sealing said interior surface from the atmosphere to form a stripping zone,   forming a stream of stripping composition in a gaseous state capable of destroying the adhesion between said coating and said interior surface, said stripping composition normally being liquid and having a partial pressure of at least about 5 mm. of Hg. at ambient temperature and pressure   introducing said stripping composition in the gaseous state into said stripping zone into contact with said interior surface at about ambient temperature and pressure, and at the same time,   withdrawing at least a portion of said air from said stripping zone so that the gas phase in said stripping zone is enriched with said stripping composition,   circulating said stripping composition within said stripping zone and,   maintaining said stripping composition in the gaseous state in contact with said coated surface at about ambient temperature and pressure and substantially in the absence of liquid stripping composition condensate on said surface until the adhesion between said protective coating and said surface is substantially destroyed.   
     
     
       15. A method according to claim 14 in which said stream of stripping composition comprises a lower chloroalkane and is formed without heating said stripping composition to reflux temperature and wherein form a major portion to substantially all of said air is withdrawn from said stripping zone so that the atmosphere in the stripping zone is mainly stripping gas, the pressure of which is such that substantially no liquid condensate forms on the surface being stripped. 
     
     
       16. A method according to claim 14 and the further steps of continuously withdrawing a portion of said gaseous state stripping composition from said stripping zone and recirculating said withdrawn gaseous state stripping composition back into said stripping zone. 
     
     
       17. A method according to claim 14 in which said stream of stripping composition in the gaseous state is formed by passing a stream of air over said stripping composition in an evaporation zone and without heating said stripping composition to reflux temperature. 
     
     
       18. A method according to claim 1 in which said stripping composition comprises a chlorinated hydrocarbon. 
     
     
       19. A method according to claim 1 in which said protective coating is paint. 
     
     
       20. A method according to claim 1 in which said protective coating comprises epoxy paint. 
     
     
       21. A method according to claim 1 in which said protective coating is residual crude oil. 
     
     
       22. A method according to claim 1 in which said protective coating is Bunker C fuel oil.